This invention is in the field of human medicine. More particularly, this invention is in the field of pharmaceutical treatment of the diseases of diabetes and hyperglycemia. 2. Description of Related Art
It has long been a goal of insulin therapy to mimic the pattern of endogenous insulin secretion in normal individuals. The daily physiological demand for insulin fluctuates and can be separated into two phases: (a) the absorptive phase requiring a pulse of insulin to dispose of the meal-related blood glucose surge, and (b) the post-absorptive phase requiring a sustained delivery of insulin to regulate hepatic glucose output for maintaining optimal fasting blood glucose.
Accordingly, effective therapy for people with diabetes generally involves the combined use of two types of exogenous insulin formulations: a rapid acting meal time insulin provided by bolus injections and a long-acting, so-called, basal insulin, administered by injection once or twice daily to control blood glucose levels between meals. An ideal basal insulin will provide an extended and "flat" time action--that is, it will control blood glucose levels for at least 12 hours, and preferably for 24 hours or more, without significant risk of hypoglycemia. Furthermore, an ideal basal insulin should be mixable with a soluble meal-time insulin, and should not cause irritation or reaction at the site of administration. Finally, basal insulin preparations that are suspension formulations should be able to be readily, and uniformly resuspended by the patient prior to administration.
As is well understood by those skilled in this art, long-acting insulin formulations have been obtained by formulating normal insulin as microcrystalline suspensions for subcutaneous injection. Examples of commercial basal insulin preparations include NPH (Neutral Protamine Hagedorn) insulin, protamine zinc insulin (PZI), and ultralente (UL). NPH insulin is the most widely-used insulin preparation, constituting from 50 to 70 percent of the insulin used worldwide. It is a suspension of a microcrystalline complex of insulin, zinc, protamine, and one or more phenolic preservatives. NPH insulin preparations are commercially available incorporating human insulin, pork insulin, beef insulin, or mixtures thereof. Also, NPH-like preparations of a monomeric insulin analog, LysB298,ProB29-human insulin analog, are known in the art [abbreviated herein as "NPL": De Felippis, M. R., U.S. Pat. No. 5,461,031, issued Oct. 24, 1995; De Felippis, M. R., U.S. Pat. No. 5,650,486, issued Jul. 22, 1997; and De Felippis, M. R., U.S. Pat. No. 5,747,642, issued May 5, 1998].
NPH insulin microcrystals possess a distinctive rod-shaped morphology of typical dimensions about 5 microns long by 1 micron thick and 1 micron wide. The extended duration of action of NPH insulin microcrystals results from their slow absorption from the subcutaneous injection site.
Therapy using currently-available NPH insulin preparations fails to provide the ideal "flat" pharmacokinetics necessary to maintain optimal fasting blood glucose for an extended period of time between meals. Consequently, treatment with NPH insulin can result in undesirably high levels of insulin in the blood, which may cause life-threatening hypoglycemia.
In addition to failing to provide an ideal flat pharmacokinetic profile, the duration of action of NPH insulin also is not ideal. In particular, a major problem with NPH therapy is the "dawn phenomenon" which is hyperglycemia that results from the loss of effective glucose control overnight while the patient is sleeping. These deficiencies in glycemic control contribute to serious long-term medical complications of diabetes and impose considerable inconvenience and quality-of-life disadvantages to the patient.
Protamine zinc insulin (PZI) has a composition similar to NPH, but contains higher levels of protamine and zinc than NPH. PZI preparations may be made as intermediate-acting amorphous precipitates or long-acting crystalline material. PZI, however, is not an ideal basal insulin pharmaceutical because it is not mixable with a soluble meal-time insulin, and the high zinc and protamine can cause irritation or reaction at the site of administration.
Human insulin ultralente is a microcrystalline preparation of insulin having higher levels of zinc than NPH, and not having either protamine or a phenolic preservative incorporated into the microcrystal. Human ultralente preparations provide moderate time action that is not suitably flat, and they do not form stable mixtures with insulin. Furthermore, they are difficult to resuspend.
There have been attempts to address the perceived inadequacies of known insulin suspensions. Fatty acid-acylated insulins have been investigated for basal control of blood glucose [Havelund, S., et al., WIPO publication WO95/07931, Mar. 23, 1995]. Their extended time action is caused by binding of the fatty acyl portion of these molecules to serum albumin. The fatty acyl chain lengths of these molecules is such as to take advantage of the fatty acid binding capability of serum albumin. The fatty acid chains used in fatty acid-acylated insulins are typically longer than about ten carbon atoms, and chain lengths of fourteen and sixteen carbon atoms are optimal for binding to serum albumin and extending time action.
Unlike NPH insulin, which is insoluble, the aforementioned fatty acid-acylated insulins are soluble at the usual therapeutic concentrations of insulin. However, the time action of these preparations may not be sufficiently long enough, or flat enough, to provide ideal basal control, and they are less potent than insulin, thereby requiring administration of greater amounts of the drug agent [Radziuk, J., et al., Diabetologia 41:116-120, 489-490 (1998)].
Whittingham, J. L., et al. [Biochemistry 36:2826-2831 (1997)] crystallized B29-N.epsilon.-tetradecanoyl-des(B30)-human insulin analog as a hexamer complex with zinc and phenol for the purpose of structural studies by X-ray crystallography. The hexamer was found to be in the R6 conformation, and to have certain properties different from hexamers of human insulin. Whittingham, et al. do not disclose any pharmaceutical or pharmacological properties of the crystal that was formed, nor do they suggest that such a crystal would have any advantageous properties for treating diabetes or hyperglycemia. It is not possible to predict from Whittingham, et al. whether protamine-containing crystals of the NPH type could be formed with derivatized insulins and insulin analogs, or what the pharmacokinetics or pharmacodynamic response of such crystals would be.
Thus, there remains a need to identify insulin preparations that have flatter and longer time action than NPH insulin, that are mixable with soluble, meal-time insulins, that can be readily resuspended, and that do not pose risk of irritation or reaction at the site of administration.